Nanophotonics and Detectors Introduction
This course dives into nanophotonic light emitting devices and optical detectors, including metal semiconductors, metal semiconductor insulators, and pn junctions. We will also cover photoconductors, avalanche photodiodes, and photomultiplier tubes. Weekly homework problem sets will challenge you to apply the principles of analysis and design we cover in preparation for real-world problems.
Course Learning Outcomes
At the end of this course you will be able to…
(1) Use nanophotonic effects (low dimensional structures) to engineer lasers
(2) Apply low dimensional structures to photonic device design
(3) Select and design optical detector for given system and application

In this module, you will learn about the basics of detection and the key performance metrics that are used to evaluate detectors including noise equivalent power and detectivity. This lays the building blocks for fundamental understanding, design, and use of different photonic detection technology. This is core information that should be in the wheelhouse of any photonics researcher or engineer.

Impartido por:

Juliet Gopinath

Associate Professor

Transcripción

I'd like to discuss the detection of light. It's just as important as the generation of light. So, the fundamental purpose of any photonic detector is to convert a photonic signal to an electrical signal. Depending on the application, the performance criteria can vary significantly. Take an imager for example. We need high spatial resolution and gray-scale resolution. It may have to operate on high and low light levels. At low light levels, the detector may need to provide some gain. At high light levels, it shouldn't be prone to image smearing. In addition, we need two-dimensional performance as well. Now, let's take the case of optical communications. In optical communications, the most important thing is to ensure signal recognition and avoid intersymbol interference. In this case, the speed of the detection is critical, and this is not so important for imaging. So, this just goes to show you that depending on your application, you'll design your detector differently. So, now let's take the case of a CCD camera, where charge is transported across the device and read at one corner of the array. What we want to do is, we want to estimate how many photons are captured and converted into electrons. So, let's start by considering a monochromatic input light level of 200 lux, which corresponds to standard room lighting. One lux is one lumen per meter square. It's a unit of optical power that's calibrated to the sensitivity of the human eye. So, at 555 nanometers, one Watt is 680 lumens. So, using this conversion, we can convert 200 lux into 0.29 Watts per meter square. So, now let's think about the fact that we have an aperture. Okay. So, essentially, now we just need to, we need to find the photon flux. The photon flux will be nothing more than the power per area, times the area, times Lambda over h_c. So, that's exactly what we do and we end up with a photon flux of 6.31 times ten to the 13th photons per second. So, now let's think about the next question which is really, how many photons per pixel per second are there? So, we take this quantity divided by the number of pixels, to get 3.16 times 10 to the seven photons per pixel per second. Now, not every photon is converted to an electron. So, if we assume a quantum efficiency of 30 percent, the number of electrons generated by the input photons is 9.48 times 10 to the six electrons per pixel per second. We can now think about the case of adding a shutter speed. So, if we add a shutter speed, we can essentially now divide this number by 30. So, what we end up with is 3.16 times 10 to the fifth electrons per pixel. So, if the light level drops to one lux, this is the light level at night during a full moon, the number of photogenerated electrons per pixel becomes 1600. So, therefore we need the detector to be capable of counting a very small number of electrons. For reliable detection, you really need the noise level to be below the lowest possible signal level.